February 2012 Issue
Table of Contents
Where Credit is Due
Mailport: February 2012
As a retired scientist that worked in and eventually managed tech centers, I read the article “The Great Titanium Trickle-Down” in the December 2011 issue with great interest. Kudos to author Patrick Childress for his insightful article. Much useful information was presented, and I’d like to make some comments.
First, drills are not made from titanium, but are coated with titanium nitride (TiN), imparting superior wear resistance, whether made from tool steels or cemented carbide. While titanium and its alloys, particularly T-6-4, offer great strength, low weight, and outstanding corrosion resistance in the marine environment, resistance to galling is very poor. TiN coatings, applied by chemical vapor deposition (CVD), solve this problem for use in rotating applications and also provide resistance to galvanic corrosion. Machining, forming, and joining of titanium alloys are, however, best left to professionals experienced in these fields. Another source of Ti-6-4 materials is aerospace companies in the form of bar ends too short for forging items like fan and compressor blades or offal from sheet-fabrication operations. A caveat, most of the bar stock may require forging to produce stock of suitable thickness for items such as chainplates, cleats, and fasteners. Again, forging operations are best left to the experts.
Glass coatings are used to prevent absorption of nitrogen during forging. Within these companies, there may also be perfectly acceptable stock for which the specs have been misplaced and hence cannot be used for flight-critical hardware. I have an assortment of such bars and have machined parts for my yacht in my home shop. All of the above materials may be available at greatly reduced cost.
Dr. Charles F. Barth
Crazy Horse, C&C 37 TR